Electromechanical switch and method of forming the same

ABSTRACT

A memory device includes a storage node, a first electrode, and a second electrode formed in a memory cell, the storage node stores electrical charges, the first electrode comprising a first portion electrically connected to a second portion, the first portion moves to connect to the storage node when the second electrode is energized.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Divisional Application of U.S. patent applicationSer. No. 12/392,780 filed on Feb. 25, 2009, now U.S. Pat. No. 7,929,341which claims priority to Korean patent applications 2008-0026812 filedon Mar. 24, 2008 and 2008-0085041 filed on Aug. 29, 2008, the contentsof which are herein incorporated by reference in their entirety.

TECHNICAL FIELD

The present disclosure relates to an electromechanical switch and amethod of forming the same, and more particularly to anelectromechanical switch having an electrode movably connected to astorage node and a method of forming the same.

DISCUSSION OF RELATED ART

Dynamic RAM (DRAM) is a solid state memory that requires refreshing tokeep the data active. A memory cell in DRAM includes a capacitor and MOStransistor. The capacitor's charge decays, due to leakage, so the systemmust periodically refresh the charge to maintain the value. The MOStransistor acts as a switch in the memory cell. If the memory is to beread, the voltage on the capacitor is detected on the data line by asense amplifier. If a write or refresh operation is called for, the dataline becomes an input line. When the proper address turns on the MOStransistor in the DRAM cell, the capacitor can be charged or rechargedfrom data-in.

One way to increase the density of the DRAM is by reducing the size ofthe MOS transistors. However, reducing the size of MOS transistorsraises other issues such as short channel or junction leakage. Anotherway to increase the density of the DRAM is by stacking multiple layersof memory cells one over another. However, when a MOS transistor is usedin a memory cell, a semiconductor substrate must be used to accommodatethe MOS transistor thereon, and the semiconductor substrate must beformed between upper and lower arrays of memory cells having the MOStransistors. A respective semiconductor substrate formed between themultiple layers of memory cells increases a thickness of the DRAM.

A need therefore exists for an improved switching device for use in amemory device.

SUMMARY OF THE INVENTION

According to an exemplary embodiment of the present invention, a memorydevice comprises a storage node, a first electrode, and a secondelectrode formed in a memory cell, the storage node stores electricalcharges, the first electrode comprising a first portion electricallyconnected to a second portion, the first portion moves to connect to thestorage node when the second electrode is energized.

The electrical charges received from the storage node can transferthrough the first portion to a voltage sensing circuit connected to anend of the second portion.

The first portion and the second portion can be connected through acontact plug.

A first end of the first portion can move from a first position to asecond position for reading out the electrical charges stored within thestorage node or for writing the electrical charges to the storage node.

The first end of the first portion can be in the second position tocontact the storage node when the second electrode is energized.

A second end of the first portion can be anchored on the contact plug.

A first distance between the first position and the second position canbe substantially the same as a second distance between the secondelectrode and a corresponding first portion of the first electrode.

A first distance between the first position and the second position canbe smaller than a second distance between the second electrode and acorresponding first portion of the first electrode.

The first portion may comprise a first layer and a second layer, thefirst layer comprising a different material from the second layer.

The first portion can be substantially shorter than the second portion.

The second electrode can be energized when a voltage is applied.

The memory device may further comprise a substrate on which the secondportion is formed, wherein the substrate comprises at least one ofglass, semiconductor, or plastic.

The storage node may comprise a capacitor including a third electrode, adielectric layer, and a fourth electrode.

The third electrode can receive the first end of the first portion andthe fourth electrode can be formed on a conductive plate.

The storage node can comprise a conductive pattern surrounded by aninsulator.

The memory device can further comprise a conductive plate on which thestorage node is formed.

The first electrode can be a bit line and the second electrode can be aword line.

According to an exemplary embodiment of the present invention, a memorydevice comprises a first memory cell having a first word line and afirst storage node that stores a first charge, a second memory cellhaving a second word line and a second storage node that stores a secondcharge, a bit line having a first portion formed in the first memorycell and a second portion formed in the second memory cell, a beam lineformed having a first portion in the first memory cell and a secondportion formed in the second memory cell, the beam line is electricallyconnected to the bit line, wherein an end of the first portion of thebeam line moves to connect to the first storage node when the first wordline is energized, and an end of the second portion of the beam linemoves to connect to the second storage node when the second word line isenergized.

The bit line and the beam line can be connected through a contact plug.

A center of the beam line can be anchored on the contact plug.

The beam line can be substantially symmetrical with respect to thecontact plug.

The first charge received from the first storage node can be transferredthrough the beam line to a voltage sensing circuit connected to an endof the bit line.

The end of the first portion of the beam line can move from a firstposition to a second position for reading out the first charge storedwithin the first storage node or for writing the first charge to thefirst storage node.

The end of the first portion of the beam line can be in the secondposition to contact the first storage node when the first word line isenergized.

A first distance between the first position and the second position canbe substantially the same as a second distance between the first wordline and a corresponding portion of the beam line.

A first distance between the first position and the second position canbe smaller than a second distance between the first word line and acorresponding portion of the beam line.

The beam line can comprise a first layer and a second layer, the firstlayer comprising a different material from the second layer.

The beam line can be substantially shorter than the bit line.

The first word line can be energized when a voltage is applied.

The memory device may further comprise a substrate on which the bit lineis formed, wherein the substrate comprises at least one of glass,semiconductor, or plastic.

The first storage node can comprise a capacitor including a firstelectrode, a dielectric layer, and a second electrode.

The first electrode can receive the end of the first portion of the beamline and the second electrode can be formed on a conductive plate.

The first storage node can comprise a conductive pattern surrounded byan insulator.

The memory device may further comprise a conductive plate on which thefirst storage node is formed.

According to an exemplary embodiment of the present invention, a memorydevice comprises a first pair of memory cells connected to a bit line,the first pair of memory cells having a first beam line, a second pairof memory cells formed adjacent to the first pair of memory cells andconnected to the bit line, the second pair of memory cells having asecond beam line, wherein each of the beam lines moves to connect to arespective storage node that stores a charge when a respective word lineis energized.

The bit line and each of the beam lines can be electrically connectedthrough a respective contact plug.

Each of the beam lines can be anchored on the respective contact plug.

Each of the beam lines can be substantially symmetrical with respect tothe respective contact plug.

The charge received from the respective storage node can transferthrough each of the beam lines to a voltage sensing circuit connected toan end of the bit line.

An end of each of the beam lines can move from a first position to asecond position for reading out the charge stored within the respectivestorage node or for writing the charge to the respective storage node.

The end of each of the beam lines can be in the second position tocontact the respective storage node when the respective word line isenergized.

A first distance between the first position and the second position canbe substantially the same as a second distance between the respectiveword line and a corresponding portion of each of the beam lines.

A first distance between the first position and the second position canbe smaller than a second distance between the respective word line and acorresponding portion of each of the beam lines.

Each of the beam lines can comprise a first layer and a second layer,the first layer comprising a different material from the second layer.

Each of the beam lines can be substantially shorter than the bit line.

The respective word line can be energized when a voltage is applied.

The memory device may further comprise a substrate on which the bit lineis formed, wherein the substrate comprises at least one of glass,semiconductor, or plastic.

The respective storage node can comprise a capacitor including a firstelectrode, a dielectric layer, and a second electrode.

The first electrode can receive the end of each of the beam lines andthe second electrode is formed on a conductive plate.

The respective storage node can comprise a conductive pattern surroundedby an insulator.

The memory device may further comprise a conductive plate on which therespective storage node is formed.

According to an exemplary embodiment, a memory device comprises asubstrate, a bit line formed on the substrate, a word line formed on thebit line, a beam line formed over the word line, a capacitor storing acharge, the capacitor formed between the beam line and the substrate,and the beam line moves to connect to the capacitor when the word lineis energized.

The memory device may further comprise a contact plug connecting the bitline and the beam line.

The memory device may further comprise a first interlayer dielectriclayer having a plurality of pores formed on the beam line.

The memory device may further comprise a second interlayer dielectriclayer formed on the first interlayer dielectric layer.

A first end of the beam line can move from a first position to a secondposition for reading out the charge stored within the capacitor or forwriting the charge to the capacitor.

The first end of the beam line can be in the second position to contactthe capacitor when the word line is energized.

A second end of the beam line can be anchored on the contact plug.

A first distance between the first position and the second position canbe substantially the same as a second distance between the word line anda corresponding portion of the beam line.

A first distance between the first position and the second position canbe smaller than a second distance between the word line and acorresponding portion of the beam line.

The beam line can comprise a first layer and a second layer, the firstlayer comprising a different material from the second layer.

The beam line can be substantially shorter than the bit line.

The word line can be energized when a voltage is applied.

The substrate may comprise at least one of glass, semiconductor, orplastic.

The capacitor may include a first electrode, a dielectric layer, and asecond electrode.

The first electrode can receive the first end of the beam line and thesecond electrode can be formed on a conductive plate.

The memory device may further comprise a conductive plate on which thecapacitor is formed.

According to an exemplary embodiment of the present invention, a methodof forming a memory device comprises forming a bit line of first cellson a substrate, forming a word line over the bit line, forming a beamline over the word line with a first gap therebetween, electricallyconnecting the bit line and the beam line, forming a capacitor betweenan end portion of the beam line and the substrate, the end portion ofthe beam line and a top surface of the capacitor having a second gap,forming an interlayer insulating layer over the beam line, and forming abit line of second cells on the interlayer insulating layer.

The first gap can be substantially the same as the second gap.

The second gap can be smaller than the first gap.

According to an exemplary embodiment of the present invention, a methodof forming a memory device comprises forming a first conductive layer ona substrate, patterning the first conductive layer to form a transistorin a peripheral region of the substrate and to form a bit line in a cellregion of the substrate, forming a first interlayer dielectric layer onthe transistor and the bit line, forming a capacitor on the firstinterlayer dielectric layer in the cell region, forming a first contactplug through the first interlayer dielectric layer in the peripheralregion, and a second contact plug through the first interlayerdielectric layer in the cell region, forming a second conductive layeron the first contact plug, on the second contact plug, and on thecapacitor, patterning the second conductive layer to form a word line inthe cell region, forming a first sacrificial layer over the word line,forming a beam line over the first sacrificial layer, forming a secondsacrificial layer over the beam line, and removing the first and secondsacrificial layers.

The method may further comprise forming a second interlayer dielectriclayer having a plurality of pores over the second sacrificial layer.

Removing the first and second sacrificial layers may comprise flowingetching chemicals through the plurality of pores.

The method may further comprise forming a third interlayer dielectriclayer over the second interlayer dielectric layer.

The first sacrificial layer can have a varied thickness. The firstsacrificial layer can have a consistent thickness.

BRIEF DESCRIPTION OF DRAWINGS

Exemplary embodiments of the present invention can be understood in moredetail from the following descriptions taken in conjunction with theaccompanying drawings, in which:

FIG. 1 is a perspective view showing an electromechanical switchaccording to an exemplary embodiment of the present invention;

FIG. 2 shows a movable portion of an electromechanical switch accordingto an exemplary embodiment of the present invention;

FIG. 3 shows a movable portion of an electromechanical switch accordingto an exemplary embodiment of the present invention;

FIG. 4 is a cross-sectional view of a memory device including a MOStransistor in a peripheral region and an electromechanical switch in acell region according to an exemplary embodiment of the presentinvention;

FIG. 5 is a cross-sectional view of a memory device includingelectromechanical switches in a peripheral region and cell regionaccording to an exemplary embodiment of the present invention;

FIG. 6 is a cross-sectional view of a memory device including a firstarray of memory cells and a second array of memory cells formed on thefirst array of memory cells according to an exemplary embodiment of thepresent invention;

FIG. 7 is a cross-sectional view of a memory device including a firstarray of memory cells and a second array of memory cells formed on thefirst array of memory cells according to an exemplary embodiment of thepresent invention;

FIG. 8 is a cross-sectional view of a memory device including anelectromechanical switch having a dimpled gap according to an exemplaryembodiment of the present invention;

FIG. 9 a cross-sectional view of a memory device including anelectromechanical switch having a dimpled gap according to an exemplaryembodiment of the present invention;

FIG. 10 is a cross-sectional view of a memory device including a firstarray of memory cells and a second array of memory cells formed on thefirst array of memory cells according to an exemplary embodiment of thepresent invention;

FIG. 11( a) through FIG. 16( b) show a method of forming a memory devicehaving an electromechanical switch according to an exemplary embodimentof the present invention;

FIG. 17( a) through FIG. 20 show a method of forming a second array ofmemory cells formed on a first array of memory cells according to anexemplary embodiment of the present invention;

FIG. 21( a) through FIG. 23( b) show a method of forming anelectromechanical switch having the dimpled gap according to anexemplary embodiment of the present invention;

FIGS. 24( a) and 24(b) show a method of forming a sacrificial layer foran electromechanical switch having a dimpled gap according to anexemplary embodiment of the present invention;

FIGS. 25( a) and 25(b) show a method of forming a sacrificial layer foran electromechanical switch having a dimpled gap according to anexemplary embodiment of the present invention;

FIGS. 26( a) through 26(c) show a method of forming a sacrificial layerfor an electromechanical switch having a dimpled gap according to anexemplary embodiment of the present invention; and

FIG. 27 shows a system including a memory device formed according to anexemplary embodiment of the present invention.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

The present invention will now be described more fully with reference tothe accompanying drawings in which example embodiments of the inventionare shown. This invention may, however, be embodied in many differentforms and should not be construed as limited to the exemplaryembodiments set forth herein.

FIG. 1 is a perspective view showing an electromechanical switchaccording to an exemplary embodiment of the present invention. Theelectromechanical switch can be used in a memory cell constituting amemory device such as, for example, a Dynamic Random Access Memory(DRAM). The electromechanical switch can also be used in electronicdevices other than the memory device.

Referring to FIG. 1, an electromechanical switch includes a firstelectrode and a second electrode disposed in a memory cell. The firstelectrode can be a word line 146 and the second electrode can be a beamline including a suspended beam line 160 and a buried bit line 110. Theword line 146 is disposed between the suspended beam line 160 and theburied bit line 110. The buried bit line 110 is electrically connectedto the suspended beam line 160 through a direct contact such as, forexample, a contact plug 136. The buried bit line 110 is disposed on thesubstrate 100. The substrate 100 may comprise, for example, glass,semiconductor or plastic.

In an exemplary embodiment, the suspended beam line 160 includes firstand second flexible extensions 160 a and 160 b extended in oppositedirections. The first and second flexible extensions 160 a and 160 b aredisposed on and anchored with respect to the contact plug 136. In anexemplary embodiment, a conductive pattern 144 can be formed between thesuspended beam line 160 and the contact plug 136. The suspended beamline 160 can be substantially symmetrical with respect to the contactplug 136. A length of the first flexible extension 160 a can besubstantially the same as a length of the second flexible extension 160b. A length of the suspended beam line 160 is substantially smaller thana length of the buried bit line 110.

In an exemplary embodiment, the movement of the first flexible extension160 a does not affect the movement of the second flexible extension 160b. For example, the first flexible extension 160 a can move downwardlywhile the second flexible extension 160 b does not move. The first andsecond flexile extensions 160 a and 160 b can be substantially straight.Alternatively, the first and second flexible extensions 160 a and 160 bcan be curved, or can have a plurality of recessed and protrudingportions conforming to the pattern of the surface disposed under thefirst and second flexible extensions 160 a and 160 b.

In an exemplary embodiment, the suspended beam line 160 comprises afirst layer and a second layer. The first layer can be laminated on thesecond layer. The first layer and the second layer can comprise the samematerial or can be made from different materials. For example, the firstlayer may comprise a silicon oxide (SiO₂) layer or a silicon nitride(SiN) layer, and the second layer may comprise a tantalum-basedconductive material such as Ta or TaN. The suspended beam line 160having two layers with different materials can be more flexible ascompared to a suspended beam line comprising a single material layer.

Between the first flexible extension 160 a and the buried bit line 110,a storage node is disposed. The storage node is an electrical node of acharge storing device. When electrically connected, electrical chargescan move through the first flexible extension 160 a and the contact plug136 to a voltage sensing circuit connected to an end of the buried bitline 110. In an exemplary embodiment, the storage node can be anelectrical node of a capacitor 152. Alternatively, the storage node canbe a node of a conductive pattern surrounded by an insulator. Thecapacitor 152 includes an upper electrode 130 a, a lower electrode 126,and a dielectric layer 128 disposed between therebetween.

The capacitor 152 can be disposed near a first end of the first flexibleextension 160 a. The second end of the first flexible extension 160 a isdisposed on the contact plug 136. The upper electrode 130 a can have,for example, a substantially rectangular shape. The first end of thefirst flexible extension 160 a can contact the upper electrode 130 a. Inan exemplary embodiment, the first end of the first flexible extension160 a contacts substantially a center portion of the upper electrode 130a. The contact can be a point, line or surface contact between the firstend of the first flexible extension 160 a and the upper electrode 130 a.In an exemplary embodiment, a conductive pad pattern 148 can be formedon the upper electrode 130 a.

With regard to the vertical direction, the word line 146 can be disposedbetween the first flexible extension 160 a and the buried bit line 110.With regard to the horizontal direction, the word line 146 can bedisposed between the second end of the first flexible extension 160 aand the capacitor 152. When the word line 146 is energized, the firstend of the first flexible extension 160 a is movably connected to thecapacitor 152. In an exemplary embodiment, the first flexible extension160 a can be connected to the capacitor 152 through the conductive padpattern 148. The word line 146 can be energized when a voltage isapplied. When the word line 146 pulls the first flexible extension 160a, a distance between the word line 146 and the first flexible extension160 a becomes closer, but the word line 146 and the first flexibleextension 160 a do not contact each other. However, the first end of thefirst flexible extension 160 a contacts the upper electrode 130 a of thecapacitor 152, or contacts the conductive pad pattern 148 formed on theupper electrode 130 a. In a data write operation, the capacitor 152 ischarged with electrons through the contact. Similarly, in a data readoperation, the word line 146 pulls the first flexible extension 160 aand the first end of the first flexible extension 160 a contacts theupper electrode 130 a, or contacts the conductive pad pattern 148 formedon the upper electrode 130 a. With the contact, the bit line senses theexistence of electrons in the capacitor 152.

A second memory cell corresponding to the second flexible extension 160b can be a mirror image of the first memory cell corresponding to thefirst flexible extension 160 a. For example, the second flexibleextension 160 b contacts a capacitor when a word line pulls the secondflexible extension 160 b. As such, the first flexible extension 160 a ismovably connected to the capacitor 152 when the word line 146 isenergized, and the second flexible extension 160 b is movably connectedto another capacitor formed thereunder when the word line correspondingto the second flexible extension 160 b is energized.

A first pair of memory cells includes a first memory cell correspondingto the first flexible extension 160 a and a second memory cellcorresponding to the second flexible extension 160 b. A second pair ofmemory cells having the substantially same structure of the first pairof memory cell can be formed adjacent the first pair of memory cells.The first pair and the second pair of the memory cells can be connectedthrough the buried bit line 110. As such, along the buried bit line 110,more than one pairs of memory cells can be connected, for example, in aregular interval. In the word line direction, more than one pairs ofmemory cells having the symmetrical extensions can be disposed, forexample, in a regular interval.

FIG. 2 is a schematic view showing a movable portion of anelectromechanical switch according to an exemplary embodiment of thepresent invention.

Referring to FIG. 2, the first end of the first flexible extension 161 amoves from a first position P1 to a second position P2 for reading outthe charge stored within the capacitor 152 or for writing the charge tothe capacitor 152. The first end of the first flexible extension 161 ais in the second position P2 to contact the capacitor 152 when the wordline 146 is energized. In an exemplary embodiment, a first distance D1between the first position P1 and the second position P2 issubstantially the same as a second distance D2 between the word line 146and a corresponding portion of the first flexible extension 161 adisposed over the word line 146. In an exemplary embodiment, the firstdistance D1 and the second distance D2 can be about 10 nm to about 15nm.

FIG. 3 is a schematic view showing a movable portion of anelectromechanical switch according to an exemplary embodiment of thepresent invention.

Referring to FIG. 3, the suspended beam line 162 includes a firstflexible extension 162 a and a second flexible extension 162 b. In anexemplary embodiment, a first distance D3 between the first position P3and the second position P4 is smaller than a second distance D4 betweenthe word line 146 and a corresponding portion of the first flexibleextension 162 a disposed over the word line 146. In an exemplaryembodiment, the first distance D3 can be about 10 nm to about 15 nm andthe second distance D4 can be about 20 nm to about 25 nm. The firstflexible extension 162 a can be prevented from contacting the word line146 when the word line 146 pulls the first flexible extension 162 abecause D4 is larger than D3. That is, when D3 is zero, D4 still canmaintain a distance. If the word line 146 contacts the first flexibleextension 162 a, damage may occur in the word line 146 and/or the firstflexible extension 162 a. An operation voltage of the memory device canbe lowered to maintain a minimum distance in D4.

FIG. 4 is a cross-sectional view of a memory device including a metaloxide silicon (MOS) transistor formed in a peripheral region and anelectromechanical switch formed in a cell region according to anexemplary embodiment of the present invention.

Referring to FIG. 4, in the cell region, trench isolations 102 b areformed in the substrate 100. The substrate 100 can be a semiconductorsubstrate. The buried bit line 110 is formed on the trench isolations102 b and the substrate 100. The buried bit line 110 includes aconductive pattern 104 and a mask pattern 108 formed on the conductivepattern 104. A first interlayer dielectric layer 114 is formed on theburied bit line 110. The contact plug 136 is formed through the firstinterlayer dielectric layer 114 and contacts the conductive pattern 104of the buried bit line 110. The conductive pad pattern 144 can formed onthe contact plug 136. The suspended beam line 160 can be formed on theconductive pad pattern 144. The word line 146 is formed between thesuspended beam line 160 and a second interlayer dielectric layer 134disposed on the first interlayer dielectric layer 114. The seconddistance d2 exists between the word line 146 and the first flexibleextension 160 a. The capacitor 152 is formed between near the end of thesuspended beam line 160 and the first interlayer dielectric layer 114.In an exemplary embodiment, the conductive pad pattern 148 can be formedon the capacitor 152. A first distance d1 exists between the suspendedbeam line 160 and the conductive pad pattern 148. The first and seconddistances d1 and d2 are substantially the same when the word line 146 isnot energized.

In the peripheral region, trench isolations 102 a are formed in thesubstrate 100. A MOS transistor including a gate electrode 106 and themask pattern 108 is formed on the substrate 100. A gate spacer 116surrounds the gate electrode 106 and the mask pattern 108. Source anddrain regions 118 are formed adjacent the gate spacer 116. The gateelectrode 106 in the peripheral region and the conductive pattern 104 inthe cell region can be made from the same layer. The first and secondinterlayer dielectric layers 114 and 134 can be formed on thetransistor. A contact plug 136 is formed through the interlayerdielectric layers 114 and 134 to contact the source and drain regions118. A conductive line pattern 150 is formed on the contact plug 136.

FIG. 5 is a cross-sectional view of a memory device includingelectromechanical switches in the peripheral region and the cell regionaccording to an exemplary embodiment of the present invention.

Referring to FIG. 5, in the cell region, the electromechanical switchsimilar to an embodiment shown in connection with FIG. 4 is formed on asubstrate 300. The substrate 300 can omit trench isolations because thesubstrate 300 can be a non-silicon based substrate. The substrate 300can comprise, for example, glass or plastic. In the peripheral region,an electromechanical switch can be formed instead of the MOS transistor.

FIG. 6 is a cross-sectional view of a memory device having a stackedstructure including a MOS transistor in a peripheral region according toan exemplary embodiment of the present invention.

Referring to FIG. 6, in the cell region, an interlayer dielectric layer204 including a plurality of fine pores 206 is disposed on the suspendedbeam line 160. A gap exists between the suspended beam line 160 and theinterlayer dielectric layer 204. In the peripheral region, the MOStransistor is formed on the substrate 100, and the interlayer dielectriclayer 204 is formed on the conductive line pattern 150. A dielectriclayer 208 can be formed over the interlayer dielectric layer 204 in thecell and peripheral regions. On the dielectric layer 208, another arrayof memory cells including an electromechanical switch is formed. Assuch, first and second arrays of memory cells are stacked one overanother. In an exemplary embodiment, additional arrays of memory cellscan be added.

FIG. 7 is a cross-sectional view of a memory device having a stackedstructure according to an exemplary embodiment of the present invention.Referring to FIG. 7, electromechanical switches are formed on thesubstrate 300 in a first array of memory cells 400. A second array ofmemory cells 500 is formed on the first array of memory cells 400. Thesecond array of memory cells 500 also includes the electromechanicalswitches in the cell and peripheral regions.

FIG. 8 is a cross-sectional view of a memory device including a MOStransistor formed in the peripheral region and the electromechanicalswitch formed in the cell region according to an exemplary embodiment ofthe present invention.

Referring to FIG. 8, the suspended beam line 164 can have a dimpled gap.That is, the first distance d3 is smaller than the second distance d4.When the dimpled gap is used in the memory device, the suspended beamline 164 can be prevented from touching the word line 146 when the wordline 146 pulls the suspended beam line 164. Further, an operationvoltage of the memory device can be lowered because the reduced firstdistance d3. In an exemplary embodiment, the suspended beam line 164includes a plurality of recessed and protruding portions conforming tothe surface formed thereunder.

FIG. 9 is a cross-sectional view of a memory device includingelectromechanical switches formed in the cell and peripheral regionsaccording to an exemplary embodiment of the present invention. Referringto FIG. 9, the electromechanical switch in the cell region includes adimpled gap between the suspended beam line 164 and the conductive padpattern 148 formed on the capacitor 152. Alternatively, theelectromechanical switch in the cell region includes a dimpled gapbetween the suspended beam line 164 and the capacitor 152 when theconductive pad pattern 148 is not formed on the capacitor 152. Theelectromechanical switch in the peripheral region includes a dimpled gapbetween the suspended beam line 164 and the conductive pad pattern 148formed on the interlayer dielectric layer 134.

FIG. 10 is a cross-sectional view of a memory device including a MOStransistor formed in the peripheral region and an electromechanicalswitch formed in the cell region according to an exemplary embodiment ofthe present invention. Referring to FIG. 10, electromechanical switchesin the first and second arrays of memory cells include a dimpled gapbetween the suspended beam line 164 and the conductive pad pattern 148.Alternatively, the electromechanical switches in the first and secondarrays of memory cells include a dimpled gap between the suspended beamline 164 and the capacitor 152 when the capacitor 152 contacts the tipof the suspended beam line 164 directly.

FIG. 11( a) through FIG. 16( b) show a method of forming a memory devicehaving an electromechanical switch according to an exemplary embodimentof the present invention.

Referring to FIG. 11( a), trench isolations 102 a and 102 b are disposedin the substrate 100. The substrate 100 comprises, for example, silicon.The trench isolations 102 a and 102 b can prevent dishing problems in asubsequent chemical and mechanical polishing (CMP) process.

Referring to FIG. 11( b), a MOS transistor 112 is formed in theperipheral region. The buried bit line 110 including the conductivelayer 104 and the mask pattern 108 is formed in the cell region. Aninsulating layer 99 is formed on the STI 102 a and the substrate 100.The conductive layer 104 and the mask layer 108 are formed on theinsulating layer 99. The conductive layer 104 can comprise materialhaving a low resistivity. The material can be, for example, metal, metalsilicide or doped semiconductor. The transistor 112 in the peripheralregion can be formed by patterning the conductive layer 104 and the masklayer 108. As such, the gate electrode 106 is formed in the transistor112. A gate spacer 116 surrounds the transistor 112. A source and drainregion 118 is formed in the substrate 100.

Referring to FIG. 12( a), the first interlayer insulating layer 114 isformed on the mask pattern 108 of the buried bit line 110 and thetransistor 112. A first electrode 120 is formed on the first interlayerinsulating layer 114. A dielectric layer 122 is formed on the firstelectrode 120. A second electrode 124 is formed on the dielectric layer122. The first electrode 120 can be a multilayer structure. The firstelectrode can include a barrier metal layer 120 a, a metal layer 120 b,a capping layer 120 c. The barrier metal layer 120 a may comprise, forexample, titanium or titanium nitride. The metal layer 120 b maycomprise, for example, tungsten. The capping layer 120 c may comprise,for example, titanium nitride. In an exemplary embodiment, thedielectric layer 122 can comprise, for example, oxide-nitride-oxide(ONO), or at least one of aluminum oxide, zirconium oxide, Hafniumoxide, Tantalum oxide, or a mixture thereof. The second electrode 124can also comprise a multilayer structure. The second electrode 124 caninclude a barrier layer 124 a and a metal layer 124 b. The barrier layer124 a can comprise, for example, titanium nitride. The metal layer 124 bcan comprise, for example, tungsten. Referring to FIG. 12( b), the firstelectrode 120, the interlayer insulating layer 114, and the secondelectrode 124 are etched to form a preliminary capacitor 132.

Referring to FIGS. 13( a) and 13(b), the second interlayer dielectriclayer 134 is formed on the first interlayer dielectric layer 114. Thefirst contact plug 136 is formed through the interlayer dielectriclayers 134, 114. The first contact plug 136 contacts the buried bit line110. In the peripheral region, a second contact plug 138 is formedthrough the interlayer dielectric layers 134, 114. The second contactplug 138 contacts the source/drain region 118. The contact plugs 136,138 may comprise, for example, Ti, TiN, W, Al or Cu.

Referring to FIGS. 14( a) and 14(b), the word line 146 and theconductive pad pattern 144, 148 are formed. A conductive layer 140 a isformed on the preliminary capacitor 132, the contact plugs 136, 138, andthe second interlayer insulating layer 134. A capping layer 140 b isformed on the conductive layer 140 a, thereby constituting a conductivepattern 140. The capping layer 140 b can enhance the contactcharacteristics between capacitors and beam lines. A mask pattern 142 isformed on the capping layer 140 b. The capping layer 140 b and theconductive layer 140 a are etched using the mask pattern 142.

Referring to FIGS. 15( a), 15(b) and 16(a), a sacrificial layer 156having an opening 158 exposing a top surface of the conductive padpattern 144 is formed. The sacrificial layer 156 is formed on theconductive pad pattern 144, 148 and the interlayer dielectric layer 154.The sacrificial layer 156 can have a different etch selectivity from theinterlayer dielectric layer 154 and material comprising the suspendedbeam line 160 formed over the sacrificial layer 154 in a subsequentprocess. For example, polysilicon, atomic layer deposition (ALD) oxide,SiGe, SiN, doped silicon, or doped silicon oxide can be used as thesacrificial layer 156. A second distance between the suspended beam line160 and the word line 146 and a first distance between the suspendedbeam line 160 and the conductive pad pattern 148 formed on the capacitor152 can be controlled by the thickness of the sacrificial layer 156.This is because the first distance and the second distance correspond tothe thickness of the sacrificial layer 156 which is removed in asubsequent process. In an exemplary embodiment, the sacrificial layer156 has a substantially same thickness throughout the entire cellregion. As such, the first and second distances can be the same.

Referring to FIGS. 16 (a) and 16(b), the suspended beam line 160 havinga high elasticity and dynamic stability is formed on the sacrificiallayer 156. The suspended beam line 160 can be a single layer structurecomprising, for example, Ti, TiN, a Ti metal alloy, Ta, TaN, a Ta metalalloy, or cabon nano tube. In an exemplary embodiment, the suspendedbeam line 160 can be a two layer structure where a first layer islaminated on a second layer. For example, the first layer may compriseSiO₂ or SiN, and the second layer may comprise a conductive materialsuch as Ti, TiN, a Ti metal alloy, Ta, TaN, a Ta metal alloy, or cabonnano tube. In an exemplary embodiment, the suspended beam line 160 canbe a multilayer structure. For example, in a three layer structure, thefirst layer may comprise SiO₂, the second layer may comprise TiN, andthe third layer may comprise TaN. The suspend beam line 160 can beanchored on the conductive pad pattern 144 formed on the contact plug136. In an exemplary embodiment, the beam line pattern 160 can beadhered to the conductive pad pattern 144 without using an adhesivebecause the adhesion occurs when the suspended beam line 160 isdeposited on the conductive pad pattern 144. The sacrificial layer 156can be removed by, for example, a wet etch process, a critical pointdryer (CPD), or a plasma chemical dry etching.

FIG. 17( a) through FIG. 20 show a method of forming a second array ofmemory cells formed on a first array of memory cells according to anexemplary embodiment of the present invention. In an exemplaryembodiment, multiple layers of memory cells can be stacked one overanother. For the first array of memory cells, an exemplary embodimentdescribed in connection with FIG. 11( a) through FIG. 16( b) can beused.

Referring to FIGS. 17( a) and 17(b), an additional sacrificial layer 200is disposed over the suspended beam line 160. The additional sacrificiallayer 200 is formed in the peripheral region and the cell region. Theadditional sacrificial layer 200 formed in the peripheral region isremoved. In an exemplary embodiment, the additional sacrificial layer200 comprises the same material with the sacrificial layer 156. Whenboth of the sacrificial layers 200 and 156 are removed in a subsequentprocess, a space is formed around the suspended beam line 160. The spaceallows the suspended beam line 160 moves upwardly or downwardly. Thespace can be a vacuum state or filled with an inert gas such as, forexample, N2.

Referring to FIGS. 18( a) and 18(b), the dielectric layer 204 is formedon the additional sacrificial layer 202. The dielectric layer 204 has aplurality of fine pores 206. The fine pores 206 can be used as pathstransmitting gases or liquids used in removing the sacrificial layers156, 202. The removed sacrificial layers 156, 202 can also betransmitted through the pores 206. For example, when the sacrificiallayers 156, 202 are removed by a wet etch process, etching chemicals canbe transmitted through the fine pores 206. Each fine pore 206 may have adiameter of about 10 nm to about 20 nm. In an exemplary embodiment, thefine pores 206 may be formed in a regular pattern. In an exemplaryembodiment, the fire pores 206 can be formed in the dielectric layer 204after the dielectric layer 204 is formed on the additional sacrificiallayer 202. The dielectric layer 204 may comprise, for example,polystyrene or polymethylmethacrylate (PMMA).

Referring to FIG. 19 and FIG. 20, a dielectric layer 208 is formed onthe dielectric layer 204 having the plurality of fine pores 206. Anupper array of memory cells can be formed on the dielectric layer (208).The substrate 100 required in the lower array of memory cells can beomitted when forming the upper array of memory cells becauseelectromechanical switches of exemplary embodiments of the presentinvention can be formed directly on a dielectric layer.

FIG. 21( a) through FIG. 23( b) show a method of forming anelectromechanical switch having the dimpled gap according to anexemplary embodiment of the present invention.

Referring to FIG. 21( a) and FIG. 21( b), the first sacrificial layer156 is formed on the conductive pad patterns 144, 148 and the word line146. The first sacrificial layer 156 corresponding to the capacitor 152is removed.

Referring to FIG. 22( a) and FIG. 22( b), a second sacrificial layer 158is formed on the first sacrificial layer 156 and the conductive padpattern 148 disposed on the capacitor 152. The first and secondsacrificial layers 156, 198 corresponding to the contact plug 136 areetched to form an opening 158. The opening 158 exposes a top surface ofthe conductive pad pattern 144 disposed on the contact plug 136. Thesuspended beam line 164 is formed on the second sacrificial layer 198and the exposed top surface of the conductive pad pattern 144.

Referring to FIG. 23( a) and FIG. 23( b), the first and secondsacrificial layers 156, 198 are removed. As such, the suspended beamline 164 having distances d3 and d4 is formed. In an exemplaryembodiment, d3 can be about 10 nm to about 15 nm, and d4 can be about 20nm to about 25 nm.

FIGS. 24( a) and 24(b) show a method of forming a sacrificial layer foran electromechanical switch having a dimpled gap according to anexemplary embodiment of the present invention.

Referring to FIGS. 24( a) and 24(b), the first sacrificial layer 156 isformed on the conductive pad patterns 144, 148 and the word line 146.Then, a second sacrificial layer 170 is formed on the first sacrificiallayer 156. A portion of the second sacrificial layer 170 correspondingto the capacitor 152 is removed, thereby forming a second sacrificiallayer pattern 170 a. The opening 158 is formed to expose the top surfaceof the conductive pad pattern 144 on the contact plug 136. The suspendedbeam line 164 is formed on the second sacrificial layer 170 and in theopening 158. Then, the first and second sacrificial layers 156 and 170are removed.

FIGS. 25( a) and 25(b) show a method of forming a sacrificial layer foran electromechanical switch having a dimpled gap according to anexemplary embodiment of the present invention.

Referring to FIGS. 25( a) and 25(b), a sacrificial layer 180 is formedon the conductive pad patterns 144, 148 and the word line 146. Theportion of the sacrificial layer 180 corresponding to the capacitor 152is thinner than the portion of the sacrificial layer 180 correspondingto the word line 146. The opening 158 is formed on the conductive padpattern 144. The suspended beam line pattern 164 can be formed on thesacrificial layer 180 and in the opening 158. Then, the sacrificiallayer 180 is removed.

FIGS. 26( a) through 26(c) show a method of forming a sacrificial layerfor an electromechanical switch having a dimpled gap according to anexemplary embodiment of the present invention.

Referring to FIG. 26 (a) through 26(c), a sacrificial layer 190 isformed on the conductive pad patterns 144 and 148 and the word line 146.The portion of the sacrificial layer 190 corresponding to the capacitor152 is oxidized. The oxidized portion 192 of the sacrificial layer 190is removed in a subsequent process. As such, the portion 190 b of thesacrificial layer 190 becomes thinner. The opening 158 is formed on theconductive pad pattern 144. The suspended beam line 164 is formed on thesacrificial layer 190 and in the opening 158. Then, the sacrificiallayer 190 is removed.

FIG. 27 shows a system comprising a memory device formed according to anexemplary embodiment of the present invention.

Referring to FIG. 27, a system 500 comprises a controller 510, aninput/output device 520, a memory 530, an interface 540, and a bus 550.The system 500 may include a mobile system such as a personal dataassistance (PDA), a portable computer, a web tablet, a wireless phone, amobile phone, a digital music player, or a memory card. In an exemplaryembodiment, the system 500 can be any system transmitting and/orreceiving information. The controller 510 may include, for example, amicroprocessor, a digital signal processor, or a microcontroller. TheI/O device 520 may include a keypad, keyboard or display. The memory 530can include, for example, a DRAM or a flash memory. The memory 530 canstore commands executed by the controller 510. The memory 530 and theinterface 540 can be combined by the bus 550. The system 500 can use theinterface 540 to transmit data into a communication network or toreceive data from the communication network.

Exemplary embodiments of the present invention provide a memory devicehaving an electromechanical switch where good retention of charges isachieved due to the low or zero junction leakage in theelectromechanical switch.

Exemplary embodiments of the present invention provide a memory devicehaving an electromechanical switch where variety types of substrates canbe used because the electromechanical switch can be formed on manydifferent types of substrates.

Exemplary embodiments of the present invention provide a memory devicehaving multiple arrays of memory cells that can be stacked. A highpackage density can be achieved in the multiple arrays because asubstrate can be omitted in between the two adjacent arrays of memorycells.

Exemplary embodiments of the present invention provide anelectromechanical switch using an electrode (e.g., a suspended beamline) as a part of the switch to open and close the circuit. As such, anadditional switch element to open or close the circuit can be omitted.

Exemplary embodiments of the present invention provide a memory devicehaving electromechanical switches which are smaller than the MOStransistors. As such, a size of the memory device according to exemplaryembodiments of the present invention can be reduced.

Exemplary embodiments of the present invention provide a method ofsimultaneously forming electromechanical switches in the cell region andthe peripheral region.

Although the exemplary embodiments of the present invention have beendescribed herein with reference to the accompanying drawings, it is tobe understood that the present invention should not be limited to thoseprecise embodiments and that various other changes and modifications maybe affected therein by one of ordinary skill in the related art withoutdeparting from the scope or spirit of the invention. All such changesand modifications are intended to be included within the scope of theinvention as defined by the appended claims.

1. A memory device comprising: a first pair of memory cells connected toa bit line, the first pair of memory cells having a first beam line; anda second pair of memory cells formed adjacent to the first pair ofmemory cells and connected to the bit line, the second pair of memorycells having a second beam line, wherein each of the beam lines moves toconnect to a respective storage node that stores a charge when arespective word line is energized, wherein the bit line and each of thebeam lines are electrically connected through a respective contact plug,and each of the beam lines is substantially symmetrical with respect tothe respective contact plug.
 2. The memory device of claim 1, whereineach of the beam lines is anchored on the respective contact plug. 3.The memory device of claim 1, wherein a voltage sensing circuit isconnected to an end of the bit line.
 4. The memory device of claim 1,wherein an end of each of the beam lines moves from a first position toa second position for reading out the charge stored within therespective storage node or for writing the charge to the respectivestorage node.
 5. The memory device of claim 4, wherein the end of eachof the beam lines is in the second position to contact the respectivestorage node when the respective word line is energized.
 6. The memorydevice of claim 4, wherein a first distance between the first positionand the second position is substantially the same as a second distancebetween the respective word line and a corresponding portion of each ofthe beam lines.
 7. The memory device of claim 5, wherein a firstdistance between the first position and the second position is smallerthan a second distance between the respective word line and acorresponding portion of each of the beam lines.
 8. The memory device ofclaim 1, wherein each of the beam lines comprises at least two layers.9. The memory device of claim 1, wherein each of the beam lines issubstantially shorter than the bit line.
 10. The memory device of claim1, wherein the respective word line is energized when a voltage isapplied.
 11. The memory device of claim 1, further comprising asubstrate on which the bit line is formed, wherein the substratecomprises at least one of glass, semiconductor, or plastic.
 12. Thememory device of claim 1, wherein the respective storage node comprisesa capacitor including a first electrode, a dielectric layer, and asecond electrode.
 13. The memory device of claim 12, wherein the firstelectrode receives the end of each of the beam lines and the secondelectrode is formed on a conductive plate.
 14. The memory device ofclaim 1, wherein the respective storage node comprises a conductivepattern surrounded by an insulator.
 15. The memory device of claim 1,further comprising a conductive plate on which the respective storagenode is formed.
 16. A memory device comprising: a substrate; a bit lineformed on the substrate; a word line formed on the bit line; a beam lineformed over the word line; a capacitor storing a charge, the capacitorformed between the beam line and the substrate, wherein the beam linemoves to connect to the capacitor when the word line is energized; and acontact plug connecting the bit line and the beam line, wherein the beamline is substantially symmetrical with resect to the contact plug. 17.The memory device of claim 16, further comprising a first interlayerdielectric layer having a plurality of pores formed on the beam line.18. The memory device of claim 17, further comprising a secondinterlayer dielectric layer formed on the first interlayer dielectriclayer.
 19. The memory device of claim 16, wherein a first end of thebeam line moves from a first position to a second position for readingout the charge stored within the capacitor or for writing the charge tothe capacitor.
 20. The memory device of claim 19, wherein the first endof the beam line is in the second position to contact the capacitor whenthe word line is energized.
 21. The memory device of claim 16, wherein asecond end of the beam line is anchored on the contact plug.
 22. Thememory device of claim 19, wherein a first distance between the firstposition and the second position is substantially the same as a seconddistance between the word line and a corresponding portion of the beamline.
 23. The memory device of claim 19, wherein a first distancebetween the first position and the second position is smaller than asecond distance between the word line and a corresponding portion of thebeam line.
 24. The memory device of claim 16, wherein the beam linecomprises at least two layers.
 25. The memory device of claim 16,wherein the beam line is substantially shorter than the bit line. 26.The memory device of claim 16, wherein the word line is energized when avoltage is applied.
 27. The memory device of claim 16, wherein thesubstrate comprises at least one of glass, semiconductor, or plastic.28. The memory device of claim 16, wherein the capacitor includes afirst electrode, a dielectric layer, and a second electrode.
 29. Thememory device of claim 28, wherein the first electrode receives thefirst end of the beam line and the second electrode is formed on aconductive plate.
 30. The memory device of claim 16, further comprisinga conductive plate on which the capacitor is formed.
 31. A memory devicecomprising: a substrate; a bit line formed on the substrate; a word lineformed on the bit line; a beam line formed over the word line; acapacitor storing a charge, the capacitor formed between the beam lineand the substrate, wherein the beam line moves to connect to thecapacitor when the word line is energized; and an interlayer dielectriclayer having a plurality of pores formed on the beam line.
 32. A memorydevice comprising: a first pair of memory cells connected to a bit line,the first pair of memory cells having a first beam line; a second pairof memory cells formed adjacent to the first pair of memory cells andconnected to the bit line, the second pair of memory cells having asecond beam line, wherein each of the beam lines moves to connect to arespective storage node that stores a charge when a respective word lineis energized; an interlayer dielectric layer having a plurality of poresformed on the first and second beam lines.